This invention relates to a process for the preparation of cyclohexyl cyclohexanone (hereinafter referred to as CHA) by hydrogenation in the liquid phase of cyclohexylidene cyclohexanone (hereinafter referred to as CHDA), which is here also understood to mean the tautomer 2-(1-cyclohexenyl)cyclohexanone, which hydrogenation is known from Japanese patent specification No. 47-16434.
The CHDA to be hydrogenated in this process can be obtained by the self-condensation of cyclohexanone according to various known methods, for instance by passing cyclohexanone through an acid ion-exchanger at 90.degree. C. and subjecting the resulting reaction mixture to distillation at reduced pressure (see German patent specification No. 857,960). Similar methods for the implementation of this self-condensation are known from Japanese patent specification No. 70-41377, French patent specification No. 2,186,456 and British patent specification No. 1,493,231.
The reaction mixture obtained in this self-condensation of cyclohexanone contains unconverted cyclohexanone. The fractional distillation further removes the water formed as a result of the self-condensation, such that the CHDA is separated off in virtually pure form.